This paper describes the use of the spectral signatures of near-infrared (NIR) absorbing cyanine dyes to quantitatively analyze their intermolecular interactions upon adsorption to colloidal CdSe quantum dots (QDs) with diameters of 2-3 nm. Spectroscopic characterization of the disaggregation of two types of sulfonate-functionalized cyanine molecules, IR783 and IR820, from H-aggregate dimers to monomers upon addition of methanol yields spectral signatures of aggregation used to analyze the response of the dyes to exposure to CdSe QDs. The spectrally distinct absorbances of the cyanines and QDs enable a factor analysis procedure that decomposes the absorbance spectrum of the QD/cyanine mixture into three distinct components-solution-phase cyanine molecules (in monomer and H-aggregate form), QD-bound cyanine monomers, and disordered, QD-bound cyanine aggregates-as a function of the molar ratio of cyanine to QD. The presence of these three distinct components strongly suggests that cyanines initially bind to QDs as either disordered aggregates (for small molar ratios of QD:cyanine) or as monomers (for large molar ratios of QD:cyanine). Quantitative analysis of the adsorption motifs of cyanine dyes on nanocrystalline semiconductors is a first step in understanding the influence of binding geometry on the rate and mechanism of charge transfer across the organic-inorganic interface within cyanine-sensitized photoconversion materials.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films